Federated Identity is typically performed through an Identity Correlation and or Identity Broker for a Federation.
A Federated Identity creates a Digital Subject which is the combination of all of an entity's Digital Identitys within the Digital Context and may include Identity Attributes from one of more Security Domains.
Federated Identity allows, assuming there are no agreements to the contrary, the Identity Provider (IDP) to perform as a Identity Broker using the attributes of the Federated Identity.
Federated Identity are created from a Federation of one or more Identity Provider (IDP) by some form of agreement or by an agreement of the Entity using Social Login.
Identity Brokers help facilitate this process by managing the integration between organizations and Credential Service Provider. Organizations connect once to the Identity Broker and accept many types of credentials, rather than managing each integration separately. However, this process presents Privacy Considerations for users as these connections can create the opportunity for an exposure of Private data, or for the Identity Broker or Credential Service Provider to track a user’s online activity.
There are many commercial options available; however, most of these options use one or more of the options discussed.